This invention relates to incremental shaft encoders, and more particularly to a gyroscopic testing technique for determining the accuracy of the encoders.
In precision guidance and control applications, the angular rotation of a shaft is converted into a digital output by an angular position transducer called an incremental shaft encoder. Typically, the encoder is a transparent disk with alternating opaque and clear segments of equal angular extent that interrupt the path of a light source to a detector. The detector produces an electrical signal that is processed to generate a sequence of pulses, with each pulse representing an increment of rotation. Such encoders appear in many guidance and control applications requiring precise angular rotation measurement. Satisfactory evaluation of the pulse-to-pulse accuracy of such encoders has been lacking due to the precision measurements required and the time involved in performing these measurements.
Because these devices are used in a variety of control applications, a system using a rate-integrating gyroscope, rate table, digital processing electronics, and statistical analysis is presented here to determine rapidly and precisely the accuracy of the incremental shaft encoder. The accuracy of the encoder is defined as the rms value of the sequence of differences between the ideal interpulse angular increment (i.e., 360.degree./N, where N is the number of pulses per revolution) and the actual increment.
There have been previous attempts to determine the accuracy of incremental shaft encoders. The present invention is a significant advancement over these former methods, which are performed manually on an optical bench. The invention is more accurate and rapid than the former pulse-to-pulse calibration procedures; it calibrates every pulse rather than averaging over a large angle.